But Stuart Andrew, Tory MP for Pudsey, played down claims that a free vote on the issue in the Commons would trigger the largest backbench revolt among Conservative MPs so far in this parliament.

"I've spoken to a number of people around the building, and I would be surprised if the figure of a hundred people rebelling was accurate. I suspect a number of people who have deep religious beliefs will rebel, and that's fine," he told Huffpost UK on Monday night.

MPs will not be whipped by the parties, in keeping with traditional conscience issues in the House of Commons. This means branding anyone who votes against gay marriage a "rebel" is technically inaccurate. But David Cameron has made it clear he supports the change, and some believe a significant revolt by backbenchers could harm the Conservative party’s modernising credentials.

However Stuart Andrew believes far fewer Tories will actually vote against the change to the law when it appears before the Commons in a few weeks' time.

"I suspect the figure will be more about thirty," Andrew told us, expecting that the change would be passed "without a doubt".

"There are more gay Tory MPs than there are in any of the other parties put together, and that's a record we should be proud of," he said, "I think it's changed so much, and David Cameron has made a massive difference to the party on these sorts of issues."

"MPs have to think of their own conscience, I'm not going to criticise them for it because it will be a very personal view. But time has moved on and the fact is that, in fairness, the government has said that no churches will be compelled to do this. If they don't want to, they don't have to."

Andrew, who has been in a relationship for ten years, is not in a civil partnership: "For me it's not massively important. Being with my partner is enough, I suppose. But I recognise that for some people, they want that marriage. And the law, as it stands at the moment is restrictive. It means the churches that want to do it, can't."

"I'd be interested to know where the figures have come from. If it's speculation by a journalist, then that's very poor. From the people I've been speaking to, I just can't see the hundred people they're talking about, because it would be most of the backbenchers, and the backbenchers I've been speaking to are supporting it."